Many conventional retinal eye examinations involve the use of eye drops which are given to a patient to force the patient's iris open (dilates the pupils). These drops are known as mydriatic eye drops. After the patient's pupils are dilated, the eye doctor then examines the patient's retina, also known as the “fundus,” with a conventional ophthalmoscope, which typically uses white light. Once a conventional eye exam is completed, the patient's pupils remain dilated for possibly hours, which may be very inconvenient for the patient and may prevent the patient from being able to drive, work, etc.
Viewing the retina and optic nerve is a basic part of both general medical exams (as performed by family practitioners, pediatricians, internists and other medical professionals) and eye exams (as performed by ophthalmologists and optometrists). As part of a general exam, the retina is the only place in the body where the practitioner can view blood vessels directly. Diseases that affect blood vessels, such as diabetes mellitus and hypertension, among others, can be diagnosed on the basis of changes in retinal blood vessels. Studies have shown that the blood vessel changes in the eye in these diseases correlate well with similar changes in other parts of the body, such as the kidney. Therefore the amount to which the vascular changes associated with these diseases has progressed can also be ascertained.
The optic nerve, which is actually a part of the brain, can also be visualized. Increased intracranial pressure (e.g., as caused by brain tumors) can often be diagnosed by seeing the resultant swelling of the optic nerve.
From the standpoint of the eye professional, specific important potentially blinding diseases, such diabetic retinopathy, glaucoma, and macular degeneration, among others, can both be diagnosed and followed by viewing the retina and optic nerve.
An instrument used to view the retina and optic nerve is called an ophthalmoscope. It may be either battery operated or powered from a transformer. In either case, only visible light is available for viewing the patient. Even with the use of filters, the light is uncomfortable to the patient, sometimes to the point of making the examination difficult or impossible. Opacities to visible light located in the lens of the eye (e.g., cataract) or in the vitreous (e.g., blood) also limit the ability to see the retina and optic nerve, sometimes totally precluding such examination.
In order to better study, document, share and record the changes seen in the retina and optic nerve, photographs of the back of the eye (called fundus photos) are frequently taken. The standard camera for doing this is a large table mounted instrument which generally uses photographic film (although digital variants have recently become available) and flash photography. Some smaller variants have been developed, but still require cables hooked to large power supplies, resulting in cumbersome units.
The large camera units generally may require the services of a professional photographer to operate, and the units may be priced in the range from $35,000 to $100,000, both of which factors limit their availability. The table mountings can make them inaccessible to wheel-chair patients, unless special table extensions are available. The cameras are rarely available for bed patients, in some instances. Also, such cameras are difficult to move from office to office, except by van.
As recognized by the present inventors, what is needed is a hand held device and method for examining a patient's retina without the need for mydriatic eye drops, so that retinal examinations can be performed quickly, accurately, and comfortably without dilation of the patient's pupils.
It is against this background that various embodiments of the present invention were developed.